Among serum immunoglobulin (Ig) classes, higher IgM and IgG levels were related to a lower risk of UTI (HR [95% CI]: 0.65 [0.38–1.09] and 0.26 [0.09–0.77]) but a relationship with IgA was observed only after preceding PI (HR [95% CI]: 0.20 [0.06–0.74]). This evidence concerns the gene CD40LG and bacterial urinary tract infection.